The proposed studies are designed to establish the structural requirements (amino acid sequence and conformation) for peptide antigens to stimulate antinative protein secondary b lymphocytes into antibody production. Epitopes of a model antigen, horse cytochrome c (cyt c), either constructed to assume native-like conformation or not, will be covalently coupled to a carrier protein and used to stimulate monoclonal anti-horse cyt c secondary B lymphocytes in vitro. A splenic fragment culture system in which B lymphocytes from a donor mouse are transferred to carrier-primed recipients will be employed. Appropriate strains of donor and recipient mice (allogeneic in the I region of the H-2 gene complex) will be chosen so that primary B lymphocyte responsiveness to the peptide antigens will not be a factor in these experiments. An understanding of protein structure that affects the ability of a peptide to stimulate secondary B cells which are more easily activated than primary B lymphocytes will facilitate similar studies on the more difficult problem of primary B cell triggering, key to the application of synthetic vaccines in medicine. Peptides thus far designed to mimic the linear sequence of amino acids within antibody binding sites on environmental proteins have been largely unsuccessful. A limitation is that, in general, linear peptides do not assume the same conformation as the corresponding segments in the native protein. Therefore, the set of B lymphocytes triggered by linear peptides are different from the B lymphocytes that would produce the desired "protective' antibodies to the native antigen. The proposed studies will examine ways to induce native-like conformation into synthetic peptides and will extend current work in this field relying on antibody (Ig receptor) binding into the realm of B cell stimulation. Information obtained will support future attempts to design synthetic molecules to be used as vaccines. In addition, studies of the effects of amino acid substitutions on secondary B cell triggering by peptides will add to our understanding of the molecular basis for immunological cross reactivity.